Key cytologic features distinguishing high‑grade serous carcinoma pleomorphism from mesothelial/reactive cells
- High-grade serous carcinoma in fluid cytology is separated from reactive mesothelial cells by malignant nuclear change: marked pleomorphism, coarse chromatin, macronucleoli, high nuclear-to-cytoplasmic ratios, and irregular three-dimensional papillary or ball-like clusters. - Reactive mesothelial cells can look alarming, but they usually keep a “windowed” spacing between cells, smoother nuclear contours, more even chromatin, and two-tone dense peripheral cytoplasm with blebs. - Psammoma bodies, mutant-pattern p53, and diffuse BerEP4 or MOC31 support serous carcinoma, while calretinin or WT1 alone can mislead because mesothelial cells also stain positive. (pmc.ncbi.nlm.nih.gov)
Cytology is the microscope read on loose cells in fluid or smears, and the core split here is malignant high-grade serous carcinoma versus benign or reactive mesothelial cells. (pmc.ncbi.nlm.nih.gov) High-grade serous carcinoma usually shows crowded three-dimensional groups, papillary fragments, or single bizarre cells with very high nuclear-to-cytoplasmic ratios. Its nuclei vary sharply in size and shape, with irregular membranes, coarse chromatin, and prominent nucleoli. (pathologyoutlines.com) (pmc.ncbi.nlm.nih.gov) Reactive mesothelial cells can enlarge and become multinucleated in ascites or pleural fluid, but they often keep softer chromatin, smoother contours, and visible “windows,” the tiny gaps between adjacent cells. Their cytoplasm is usually denser at the edge, lighter around the nucleus, and may show blebs rather than true tumor papillae. (pmc.ncbi.nlm.nih.gov 1) (pmc.ncbi.nlm.nih.gov 2) Architecture helps when single-cell atypia overlaps. Serous carcinoma tends to form tight cannonball-like clusters and branching papillary groups, while mesothelial proliferations more often make flat sheets with knobby borders and intercellular spacing. (pmc.ncbi.nlm.nih.gov 1) (pmc.ncbi.nlm.nih.gov 2) Background clues also matter. Psammoma bodies, the laminated calcified spheres classically linked to serous tumors, support serous carcinoma when they appear with malignant cells, but they are not sufficient on their own. (pathologyoutlines.com 1) (pathologyoutlines.com 2) Immunostains are the backstop when morphology is limited, especially on scant cell blocks. BerEP4, MOC31, and claudin-4 favor epithelial carcinoma, while calretinin, D2-40, and CK5/6 favor mesothelial cells. (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov) WT1 is useful but not decisive by itself in this exact differential. High-grade serous carcinoma is commonly WT1-positive, yet mesothelial cells can also express WT1, so the stain has to be read with morphology and a broader panel. (pathologyoutlines.com) (pmc.ncbi.nlm.nih.gov) p53 can add another layer. An aberrant overexpression or complete-null pattern supports high-grade serous carcinoma, whereas reactive mesothelial cells show a wild-type pattern instead of a mutation-pattern result. (pathologyoutlines.com) (pmc.ncbi.nlm.nih.gov) The practical read is to trust the combination of pattern and nuclei, not pleomorphism alone. Marked anisonucleosis, coarse chromatin, and disordered three-dimensional clustering push toward high-grade serous carcinoma; windows, two-tone cytoplasm, and smoother nuclei pull back toward a reactive mesothelial process. (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov)
